How to create a new condition type for palets

Hello Gurus,

I want to create a new condition type to order material palets (like LP02) but I need to calculate a discount in % for entire palets only.

By example:

A discount of 5% for each completed palets.

I order 1 palet for 100euros, I want a discount of 5 euros, and final price is 95euros.

I order 1,5 palets for 150 euros, I want a discount of 5 euros and final price is 145 euros (100-5% + 50) and not 142,5euros (150-5%).

I order 2 palets for 200 euros, I want a discount of 10 euros and final price is 190euros

I tried with a fixed amount calculation type and it works fine, I have a discount only for entire palets. But when I tried with percentage calculation type, it doesn't work.

Any Idea?

Thank you for your help

Gregory